[Elixir][Ecto] Copy an existing Ecto struct (Repo.build_from/1)

repo.ex

defmodule Repo do
  use Ecto.Repo,
    otp_app: :my_app,
    adapter: Ecto.Adapters.Postgres

  def build_from(struct) do
    struct = Ecto.put_meta(struct, state: :built)
    
    :primary_key
    |> struct.__struct__.__schema__()
    |> List.foldl(struct, &(Map.put(&2, &1, nil)))
  end
end